i remember many situations in world of warcraft where the authentication servers were down, but not the actual play servers.
if diablo servers are organized the same, you app might have a "sound" option, if run in the background of a diablo game, to warn not to disconnect.
probably useless, but i guess that would be the kind of "functionality" that would qualify as "need" instead of "want".
PS: i read your explanations and all, but i won't allow your app to check battle.net domain.
just isn't worth the risk.
but i applaud the thought AND the work